Figure 2: Radiosensitivity is associated with a differential antitumour immune response.

(a) CD3 T-cell (arrows) immunohistochemistry 10 days after 12 Gy of radiation reveals increased infiltrates with and without radiation in Py117 compared with Py8119 tumours (scale bar, 100 μm). (b) Dissociated tumours analysed by flow cytometry had a greater proportion of CD45⁺ leukocytes after radiation in the Py117 tumours. (c) Quantification revealed an influx of leukocytes after radiation in Py117 tumours but not in Py8119 tumours (4–5 mice per group). The Py117 immune infiltrate consists of CD8⁺ T-cell influx (d), no change in CD4⁺ T-cells (e), a decrease in immature myeloid cells (iMCs: CD45⁺CD11b⁺Gr1^hi) (f), and an increase in macrophages (CD45⁺CD11b⁺F4/80⁺) (g), with little differences in Py8119 tumours. (h) Implantation of tumours into nude mice revealed a decreased radiation response in Py117 tumours compared with syngeneic C57Bl/6 host and Py8119 curves were no different regardless of the host (Bold curves=repeated measures curve, thin curves=each mouse, five mice per condition). (i) MHCI (H-2Kb) is expressed on dissociated Py117 CD45⁻ cells at 10 × greater levels than in Py8119 tumours. (j) PD-L1 expression increased on dissociated Py117 CD45⁻ cells after radiation but not Py8119 cells. **P<0.007, ***P<0.0003 by two-way analysis of variance. *P=0.028 by repeated measures. All error bars, mean and s.d.